As an example of a conventional capacitor, a tantalum solid electrolytic capacitor is described below.
FIG. 3 is a cross-sectional view of the conventional tantalum solid electrolytic capacitor. A tantalum lead wire 1 and a sintered body 2 produced by sintering a mass of molded tantalum powder are joined together. A graphite layer 3 is formed on a surface of the sintered body 2, and a silver layer 4 is formed on an outer surface of the graphite layer 3. An electrode 5A is connected to the tantalum lead wire 1, and an electrode 5B is coupled to the silver layer 4. An electrode body thus produced is covered with a resin package 6.
A manufacturing method of the capacitor is demonstrated below.
First, mold a mass of tantalum powder placed around the lead wire 1 at high pressure, and sinter this molded powder to make the sintered body 2. Then, anode-oxidize the sintered body 2 in a phosphoric acid solution, and produce a dielectric film of tantalum pentoxide on a surface of the body 2 (not illustrated). Next, fill cavities of the sintered body 2 with a solid-electrolyte of manganese-dioxide or the like (not illustrated), and successively form the graphite layer 3 and the silver layer 4 on the surface of the sintered body 2. Finally, connect the electrode 5A and the electrode 5B to the tantalum lead wire 1 and the silver layer 4, respectively, and cover an outer surface of this electrode body with the resin package 6.
The manufacturing method of the sintered body 2 used in the capacitor is disclosed in Japanese Patent Laid-Open Application No. S63-262833, as an example. More specifically, the method includes steps of mixing camphor grains having a specified mean diameter with a metallic powder, press-molding this mixture and evaporating the camphor by heating. A porosity ratio of the sintered body is up to about 75%. Because a surface area of the dielectric film is small, a large capacity is hardly obtainable.